net-im/nheko: add missing dependency

At runtime, qt5-graphicaleffects are needed to display anything
in the timeline (e.g. a conversation in a room). Even the loading-
spinner isn't shown without it. Demonstrated by trying to run
nheko in a "bare" machine with just XOrg and twm.

PR: 256839
Reported by: Filipe da Silva Santos

[[ Cherry pick is not exact because quarterly has an older version,

but the runtime requirement is still there. ]]

(cherry picked from commit e0f0a32d502af6eb619fd0c377de644492673fa4)